E74 code no power to rh wire.

[Steveoarroyo]

Just installed a new nest gen 3 learning thermostat on 01/14/2022 which went without a hitch and worked fine until this morning. My house was cold and my nest thermostat did not show any temperature. It had a e74 code, no power to RH wire. Reset my  power and it came on for a short but it failed just minutes later. Tried again and it did not work at all with the same code. It should not be doing this and I have seen other postings with this issue. I had to install old thermostat to get my heater to work. There is no reason or excuse why this thermostat which is not cheap should present these issues. Would like to know if there is a solution for this problem since I am not the only one experiencing this problem.

[Mel917]

Google, I don’t care that I received a reply badge! I need my a/c to work. 

[504creole]

Try moving to Rc.

[Xinyuwang]

tried to move wire to RC but shows e73 issue.

Does this mean i need to buy a new one? Is that someone please help! Winter is coming and it is so cold in Canada.

Thank you!

[Yeagera55]

I am also having the same issue help!! I don’t even know who the hire to come help either 

[504creole]

Nest support chat won't help unless the error is active. The problem with that is you may not realize the error is there or can catch it in time to get to nest. The error happens randomly and the duration is also random in my experience.

If you've tried both R terminals to rule that out and made sure your wire connections are good and it's still happening then make sure your drain pipe isn't clogged and tripping the float switch/overflow switch.

[Xinyuwang]

Hi, finally I solved this issue and my e74 issue was caused out off power, we checked circuit breaker and move it back to normal. Then we fixed issue

[504creole]

My error would come and go. So I knew it wasn't just the breaker. But I did even try flipping it off/on. Wasn't it. Glad you got it fixed!!

[Xinyuwang]

May I ask have you solved this issue? This happened to me either.

If you solved, may I ask how you solved?

thank you! Cynthia

[504creole]

Still monitoring but I think I have. I even bought a new thermostat and swapped everything out yet it still occurred. At that point I realized it was in the house and not with Google/Nest. It's weird though that so many people have and are experiencing this same thing "at the same time".

My issue seems to be with that float switch. I had a tech check my AC but he missed that. I called back and another tech came out. Checked voltage, wiring, etc. Took it all apart. Then he got to my drain pipe and realized there was water in it. Not much tho as my nest was working of course when he showed up. But he came to the conclusion that it was intermittently filling up and tripping the switch. Glad that works! Don't need a leak in my ceiling. Lol.

[Coburn131]

I'm getting an E74 code no power, and the thermostat itself won't stay charged longer than 5 minutes! I've done all can do, the circuit breaker is good and the wiring is all correct, I've talked to several people today and still no heat! I'm taking this junk back to the store and buying the Ecobee brand, I'm just tired, frustrated, and cold! 

[504creole]

How old is it? Will it charge direct with USB? 

[Yaya1231]

Same issue every day. Pull it out and reinstall it to be normal，I will return it . 

[Cad3]

Same issue for me. Brand new Nest I installed 1 month ago. New furnace 2 years ago. Yesterday woke up cold because the nest said it didn’t have sufficient power.  Charged it and it worked. Then today woke up cold because it says no power to rH wire. Reset the breakers, rewired the thermostat, still doesn’t work.

[Alvoda01]

Same issue here,  got E74 error.  All voltage checked out at thermostat.  Used alternate thermostat without any issues.  Support told me the thermostat was bad and that I should buy a new unit. 

[Syd1]

Rh wire was not connecting to google nest 3rd gen initially. Tried just connecting the WGRhY wires and not connecting the blue C wire and it worked for some reason! 

[DQP]

I am also having problems with E74 and report of no power on Rh. In this case, it is one zone in a six zone radiant heat boiler system. Worked for a bit. The base by itself got into a state where *it* was calling for heat. I removed the baseplate and verified that connecting the W1 and Rh turned the zone on. I installed a new gen3 thermostat and see the same thing. I suspect that there is some complexity in the device including baseplate that makes it a bit unstable. I am going to try to cycle power on the system in a bit and see if that cures this zone or perhaps breaks others.

[handywowan]

https://m.youtube.com/watch?v=CRhN90XMrKU&feature=youtu.be

condensation on your hvac

[Yunger02]

Same issue.  Worked fine for two years or so and then suddenly e74 error out of the blue.  Won’t take a charge neither.  Seems like Google ought to figure this out.

[fakeusername]

This just happened to me and I was able to fix it, so I wanted to post here in case it helps anyone.

Note that I have a heat pump in my house and my Nest is configured in heat pump mode.

The issue presented as "No power to rh wire". The solution wound up being two things combined:

1. One of the other wires, the W1 wire, wasn't all the way pushed in on the Nest base. Note that Nest said that it was plugged in. What I learned from this is that a wire that isn't all the way pushed in can cause "flickering voltage", which can provide sporadic incorrect voltage from Rh to other wires. This results in the heat / cooling not turning on
2. The heat pump has two fuses, and the low-voltage fuse was blown rather than the high voltage one. The low-voltage fuse is for the signal wires (Rh, etc). The high voltage fuse is for the main power (the 240V main that comes from the circuit braker).

Here's how I diagnosed the issue:
1. I confirmed with a voltmeter (one of the ones that senses magnetic fields) that Rh did, in fact, have no voltage.
2. The technician checked the heat pump and confirmed that the Rh wire coming from the heat pump didn't have any voltage.
3. We discovered and replaced the blown fuse
4. After replacing the fuse, the fan would work, but heating and cooling would not turn on. The Nest said that heating and cooling was working.
5. We checked the coolant, fan, main board, etc on the heat pump and didn't see anything.
6. We noticed that some of the reading coming from the Nest were reading as 20v rather than 24v (this is the Rh wire connecting to the signal wire, which turns on heating / cooling).
7. We noticed that the LED on top of the nest would blink orange, than green.
8. We were not sure if (6) indicated an error, but we decided to double-check all the connections on the Nest Base.
9. Once we pushed in all the connections *firmly* so that the holds were *depressed a lot*, the cooling / heating worked.

We can't be sure, but our theory is that if the wires are not *firmly* pushed into the Nest, it will fail to consistently push the correct voltage from Rh to the signal wire, and not show any error. If the heating system doesn't get exactly the right voltage, it won't clear a high enough signal to turn on.

Note that the Nest has a menu where it will show you the voltage coming into and from each wire. Check that these values are the expected values for your heating system. If the voltage is wrong, it likely won't turn on.

[Dakota62]

HVAC tech here, there is no universal fix for this problem, it can be many things. The code means your nest isn't getting 24v power from the heater. Could be as simple as a clogged drain that is tripping the float switch or as bad as a blown transformer.

[Bruce5]

I had this same problem and the solution - once I found it - took 1 flip of a switch.  In my system, there's a "condensate pump" (this one or something that looks exactly like it).  I saw some comments on this page about cleaning it out, and then found a good video showing how to do this.  

As I sat down to start the cleaning process, I noticed that the reset button where this unit it plugged in was popped out.  I pushed it, and bam, the pump AND my thermostat started up!  

Problem solved. phew.  

[Jagnme]

The fix for no power to Rh wire for me was the float.   The water drain needed to be cleaned out.